Install Nagios Core

Download the source code for the latest stable release of Nagios Core. Go to the Nagios downloads page, and click the Skip to download link below the form. Copy the link address for the latest stable release so you can download it to your Nagios server.

At the time of this writing, the latest stable release is Nagios 4.1.1. Download it to your home directory with curl:

Once you are done installing and configuring NRPE on the hosts that you want to monitor, you will have to add these hosts to your Nagios server configuration before it will start monitoring them.

Add Host to Nagios Configuration

On your Nagios server, create a new configuration file for each of the remote hosts that you want to monitor in /usr/local/nagios/etc/servers/. Replace the highlighted word, “yourhost”, with the name of your host:

sudo vi /usr/local/nagios/etc/servers/yourhost.cfg

Add in the following host definition, replacing the host_name value with your remote hostname (“web-1” in the example), the alias value with a description of the host, and the address value with the private IP address of the remote host:

With the configuration file above, Nagios will only monitor if the host is up or down. If this is sufficient for you, save and exit then restart Nagios. If you want to monitor particular services, read on.

Add any of these service blocks for services you want to monitor. Note that the value of check_command determines what will be monitored, including status threshold values. Here are some examples that you can add to your host’s configuration file:

If you’re not sure what use generic-service means, it is simply inheriting the values of a service template called “generic-service” that is defined by default.

Now save and quit. Reload your Nagios configuration to put any changes into effect:

sudo systemctl reload nagios.service

Once you are done configuring Nagios to monitor all of your remote hosts, you should be set. Be sure to access your Nagios web interface, and check out the Services page to see all of your monitored hosts and services: